"Some background: she is a 7 month old spayed female, UTD on shots and vaccines including Bortadella and had her last Revolution treatment 2 weeks ago. "
that is in essence an assualt on her young physical self - at a key time when there are already demands just for growth .
If I interpret this correctly she is 7 months now and was " When she was spayed a month, month and a half ago" so she was 5 1/2 months at time of spay !!!!
The yellowish bubbly stool usually indicates some form of a bacterial infection. The dog was probably on a dose of antibiotics after the spay surgery .
" her poop was ok after her spay surgery, but quickly changed to loose poop "
This along with stress (physiological) along with the vaccine protocol and Revolution -- leading up to chronic malabsorption - indicated by the watery stool (rapid elimination) and yellow colour. The foamy or bubbly indicates bacterial infection of some sort.
She needs to be fed the best clean protein . She needs to detox . To fight the bacteria she needs full spectrum PROBIOTICS